Composite materials, such as fiber-reinforced materials, are being rapidly adopted for many new applications because of their light weight and exceptional strength. Some application examples include aerospace components (e.g., aircraft tail components, wing structures, fuselage skins, propellers, and the like), boats (e.g., hulls), bicycles (e.g., frames, sprockets), automotive (e.g., body panels, structural components, gas tanks), and the like. However, forming hollow cavities or channels at interfaces of composite structures still proved to be difficult. Specifically, it is desirable to cover a cavity with an uncured composite structure, which may be also referred to as a “green” composite structure. When the composite structure is uncured, it may be easily conformed to a surface of the structure having the cavity. As such, there is no need to develop different molds representing surfaces of different structures with cavities. Uncured composite structures may be initially formed on flat molds prior to applying to any curved surfaces. However, high pressures used for curing and consolidation of the composite structures tend to force these structures into any available cavities disposed on the underside of these structures effectively closing or “filling” these cavities